Large turbine generators are typically cooled by forcing a stream of a cooling fluid, such as hydrogen, over the heat producing parts of the machine. FIG. 1 illustrates a conventional hydrogen-cooled generator 10. The generator 10 includes a rotor 11 and a stator 12 enclosed by a generator frame or housing 13. The rotor 11 generally includes a set of blades 14 for propelling hydrogen around the interior of the generator 10 to promote cooling, as indicated by the directed line segments 15 illustrating typical flow patterns for the hydrogen.
Because of the high flux densities present in the core of such a machine, localized overheating may cause degradation of the insulation disposed on the laminations and end turns. In addition, ventilation bypasses or blockages, cracked conductors, shorted laminations, or other malfunctions may contribute to overheating within the generator. Because of the potentially catastrophic consequences of such overheating and degradation, it is desirable to provide an early warning of an overheating condition.
Apparatus such as the generator condition monitor has been developed to provide early warning of an overheating condition. The generator condition monitor is a highly sensitive device which rapidly detects the presence of particles in the hydrogen atmosphere of a turbine generator. Operation of the generator condition monitor is based on the principle that very high concentrations of submicron particles are produced whenever any material within the generator is heated sufficiently to initiate thermal decomposition. When an overheating situation arises within the generator, organic materials in the overheated area are affected first and degrade, producing particulates which enter the gas stream. In conventional practice, special organic compounds may be deposited throughout the generator which particulate at much lower temperatures than most organic materials utilized in usual generator construction.
In one well known generator condition monitor, submicron particles are detected by their influence on the output current of an ion chamber which is arranged to collect the hydrogen ions which are produced by a low level radiation source in the hydrogen gas stream which carries the particles. In the absence of the particles, almost all of the hydrogen ions are collected, resulting in maximum output current of a magnitude determined by the strength of the radiation source and the ionization properties of the gas stream. With particles present, some ions combine with the particles and, because the particles are much larger than the ions, the mobility of the resultant charged particle is less, and relatively few are collected in the ion chamber. The result is a decrease in the output current of the ion chamber, this decrease being a function of the particle concentration and particle size. Such an arrangement is disclosed by Grobel et al. in U.S. Pat. No. 3,427,880, which patent is incorporated herein by reference.
In the past, it has typically been necessary to remove gas from the generator for analysis to determine the level of particulates in the gas. Piping would carry the pressurized gas from the generator to the measuring device which then had to be located nearby. In the case of a hydrogen cooled generator this would extend the hydrogen zone, require expensive hydrogen explosion proof piping and ion chamber assemblies, and introduce the danger of gas leaks. For air cooled generators expensive piping and generator modifications are required. For both air and hydrogen, this moved the measuring device farther from the source of the particulation which decreased the sensitivity of the measurement. Attempts to move the location of the measuring device inside the generator were complicated by the device's need for power, and by the proximity of high voltage generator components. For example, U.S. Pat. No. 6,998,618 provides a condition monitor in which the detector component of the monitor is located within the generator, but which may still require power lines to pass through the generator housing to power the monitor. There are minimum strike distances that must be maintained inside the generator; and it is generally not acceptable to locate metallic power cables for generator condition monitoring devices near the high voltage components that cause the particulation.
Accordingly, there continues to be a need for a generator condition monitoring system that permits the measurement device or sensor for detecting particulation in relatively close proximity to high voltage generator components.